Tire retreading method



July 14, 1936. J. c. HEINTz TIRE RETREADING METHOD Filed June 20, 1935 w firm/MP' Patented July 14, 1936 U N :I T ED `S 'S PATENT OFFICEv 5 Claims.

This invention, which relatesto Afull-circleretreading of pneumatic tires, has among its objects to save time and labor in selectingthe proper size of vulcanizing mold cavity for the reception of a particular tire to be retreaded, toreduce the amount of equipment required-to handle the different sizes of tires, to avoid the complication and expense of la vulcanizer` havingadjustable width-varying means, to insure the proper performance ofthe retreading operation without producing defects such as buckling of `,the tire Walls from using a moldwhose cavityfis-too small for the tire, orobtaining spongy treads by using too large a mold cavity, toldispense with the necessity for Vspecial measuring devices, and to simplify and reduce the number of tabular instruction charts furnished by the equipment manufacturer to beconsulted by theoperator in selecting `a mold having the proper: size cavity. g

The performance vof my improved method in `connection Awith oneftype ofjretreadingyulcan- .izer'and instruction chart `is illustratedin l companying: drawing vwherein Fig. 1 is a ldiametric section of the .retreading :vulcanizen with partsromitted, and `a tire. therein.

Fig. 2 is a fragmental view-,of the form of tabular instructionjchart. 1 f, l

,Fig. 3 is afperspectiveview of a tireandmeasuring` tape illustrating the performance of the measuring step.

It is well known thatused pneumatic tires of any given nominal `size `which lmay yhave been originally of substantially the .same dimensions will, through variations .of -stretch 4in, :service, acquire `more or -less :growth -and'lbecomerfof edifferent sizes, while someof themfrmayfnotgrow appreciably before fthe :original tread `wears 01T or has-` become :so injured ras to "requireeplacegpreferred `ment. Obviouslyy theibest retreading 'resultsrcannot beobtained lwhereit is attempted to .use 1.a Vsinglevretreading moldof fixed size completely enclosing the-cross sectionof the tire, for-any `given nominal size,` likefthat inrwhich :the tire was originally vulcanized; -and further-more, to

heat `the side walls ,of theti-reztofa vulcanizing temperature Vwhere #not :protected 'fby 'the Vnew tread tends to overcureand injure the sidewalls.

These "factsihave `led yto Vthe Iadoption -of fullcircle Aretreading Imolds Asuch nas :that described Y in `my lPatent No. l1,810,963 riof VaIune `23, 1931,

wherein the walls ofthe ,-'moldV cavity embrace ronly the tread anda; portion cof the v-side ;wal1s `of an inflated, lrimemounted..tire,.annular :side .portions of the1tireacoritacting Ecavity 'walls :are

\ ztreaded,the :same f being mounted on aroadxrim `unconiinedportions of the tirewalls, will usually accommodate, in oneproperly. selected. mold cavity of fixed size, all of the lvariationsin di- 1Q mensionsof any given rated size of tire, and frequently also in thersame cavitywillV accommo- -date from two up to five different rated sizes and their several growth Variations.` .By .changing matrices or portions thereof, 4as by using ,1x5A spacer rings of dilerent Widths, `where there is 4nottoo v,much variation inV the tread diameter,

the same vulcanizer can further be accommodated to an additional range oftire sizes. VThe flexibility ofsuch equipment reduces. the opera- 20 `tors investment in mold-equipment required to handle the large number of tirelsizes and `tread .designs met .with inthe retreadingbusiness.

. My;` present invention can'vbe carried out `with that type of vulcanizer and with many similar 25 or vother types, particularly :where they ,permit `free bulging of the base portions `of, thetire fwalls. l

In the use of such equipment as heretofore practiced, I have found that while fan experi30 `enced operator may, with smaller lor `mediumsized passenger-car tires, learn to rate the size -ofa tire which may properly be'retreadedfin a particularfsize of mold, this is `very ldiicult -in the larger sizes of both those and bus and truck "'35 Vtires where comparatively large dimensional-va- `riations Vmay escape accurate estimation, and leven a skilled operator may sometimeslose a tire vby 1a :wrong estimation or making improper Yor insuflicient'measurements. i 40 vMy present invention provides -an improved "methodfincluding a new form'of tire measurement and ra new mode of predetermining'the zrelation thereto, within certain permitted limits ofitire-size variation, of a full-'circle retread mold 45 cavity of xed size, whereby the personallfactor of the operator is practically eliminatedptabulation .charts and measurements are simplified and the operator may, by carrying outi :aseries -of 'simplesteps according to the instructions furnished, `:insure himself completely against ,loss `of tires by `failure `to .'t them in `the proper molds.

In the fdrawing, '.I'U'isthe tirefcasingtoabefzre- 55 Il, together with an inflatable inner curing tube I2, and having a raw rubber tread I3 cemented upon its carcass from which the remains of the old tread have been removed. The new tread strip material is known as Camelback, and the proper dimensions of strip to give the desired width and thickness of vulcanized retread should be known to the operator and may be selected with the aid of a suitable instruction table. I4 is an ordinary non-stretchable measuring tape employed as hereinafter pointed out.

The full-circle vulcanizer shown in Fig. 1 comprises a horizontal annular holder I5 having'a peripheral chamber I6 for containing a heating iuid such as steam, a cylindrical inner chamber wall for transmitting the heat to the segmental side matrix rings I1 and the segmental middle or spacer ring I8 which collectively constitute the tread-molding portion of the mold, a pairof continuous upper and lower side-wall rings I9, 20 which are slightly spaced from the inner margins of the matrix rings I'I and maintained below a vulcanizing temperature, and a lower shelf 2l for supporting the mold, together with a series of vertical screw clamps 22 at spaced positions 22a, carried by removable holders (not shown) on the Yupper side of the chamber I6 and bearing on the upperside-wall ring I8 for holding the assembly of mold rings down against the lower shelf The several matrix, spacer and side-wall rings define a mold cavity of fixed dimensions whose 'parallel tire side-wall contacting portions on the rings I9 and 20 are maintained in alignment or proper contouring registry with the adjacent marginal molding portions of the matrix rings I1, and in tangent or parallel relation with the tire sides when in the mold. The included fixed diametric periphery or solid contour of the molding'cavity and central space as a whole is then defined in a radial plane by the inner faces of the mold rings and by the parallel spanning'lines 23, continuing the side-wall tangents from the inner faces of the rings I9 and 20 across the intervening central space. From this dimension there s omitted the changeable contour of the free base portions 24 of the tire side walls between the rim I I and the rings I9 and 20, which provide bulges in said side walls, giving or taking more or less of the total cross-sectional volume of the inflated tire according as said volume may vary in the particular tire with relation to the vsize of the confining mold cavity. Y

By having this included mold-cavity periphery predetermined and recorded and properly related to a corresponding diametric peripheral measurement taken on the tire to be vulcanized in the mold, the operator is enabled unfailingly to select the size of mold cavity which will properly fit the particular tire or other tires of different sizes within a permitted range of variation.

Fig. 2 showsv a portion of a tabulation chart furnished to the operator by the manufacturer of the vulcanizing equipment as an aid in carrying out this invention. VWithin its vertical height and its several columns it may contain all of the several tire and rim sizes used on passenger cars, for example, or on truck tires, which the repair man or tire manufacturer will be called upon to treat, together with equipment makers numbers or other symbols for identifying the sizes of vulcanizer, size'or type of matrix, spacer'and sidewallring's, and size or shape of tread material for the several tires, and a column of matrixlimits s tati'ng'thel rangeV of diametricj peripheral meas- .ifurements of. tires to ffit'sa given moldcavity., to-

'other columns opposite these tire sizes.

ywhole range of passenger-car tires, and each such size will have two or three sizes or types of the matrix rings I1 identiied in column B entitled Matrix No. Column C, Spacer No. identifies the proper spacers I8, each corresponding to one or more tire sizes. Column D is for the Tire size, column E for the Rim size, column F for Camel-back or tread I3, column G for Matrix limits and column H for Sidewall ring No. I9

The signicant limits of tire dimensions pertaining to this method are found in column G,

YMatrix limits wherein, for example, the limits 635/8"-655/8 are marked opposite the two tire sizes 5.50-17 and 625-16. This means that any tire of rated 5.50Vinch width and 17 inch bead-seat diameter, or any tire of rated 6.25 inch width n inch bead-seat diameter, having anv and 16 included diametric peripheral measurement of not less than 6315/8 inches and not more than 655/8 inches will properly fit the mold cavity provided by the matrix rings, spacer ring and u in the side-wall rings which are identified If the tire dimension is greater than the upper limit,

the cavity width should be increased by using a wider spacer ring I8, or wider matrix rings I1, and vice versa for a dimension smaller than the lower limit, as will be directed by proper instructions on the chart. In like manner the proper 'limits will be allotted to each set of cavity-defining rings for the other tire sizes, where in some cases there will be only one set of limits for one tire size and in others sometimes as many as five tire sizes, all for one mold cavity. These Matrix limitsl given in column G are predetermined by the maker of the vulcanizing equipment, from 'trials of the various actual sizes of tires which can properly be accommodated in each of the various mold-cavity sizes, consistently with good retreading results, using tread material of a size and y,shape given in column F. The chart table 25 gives the'recommended dimensions of Camelback or tread material corresponding to the several letter symbols in this column.

In practicing this method in its preferred form, a rim-mounted tire bearing a raw tread of the proper volume is inflated to a given pressure such as 25 pounds per square inch, and with the steel tape I4 its included diametric peripheral measurement is taken around the tread and along lines tangent to the side walls as shown in Fig. 3.

The tire is then fitted in a mold having a cavity whose matrix limit dimensions given in column G of the chart include this dimension of the tire, it is inflated to the proper curing pressure such as pounds for passenger-car or 150 to 200 pounds for truck tires, and vulcanization of the tread proceeded with as previously indicated and as described in my Patent 1,810,963.

l 'Someof the'steps inthe complete method as thus described maybe more or less varied. Forv example, vtheztirel could. `be measured, somewhat" 75 less accurately, without a rim and Without ination. It could also be measured diametrically around the crown of a stripped carcass Without the tread] substantially in the manner described for the tread-bearing tire, either with or Without rim-mountingand inflation, and. the limit dimensions given in column G of the chart correspondingly changed, if the operator were then sufficiently careful in his selection of the proper tread. It is also to be understood that While a preferred form of mold has been illustrated and described, the invention, broadly considered, may be practiced with any suitable mold.

It is found that this method Will afford proper retreading in practically all cases, the results are superior to those of methods involving the measurement of the tire-Wall sectional contour from bead to bead and adjustment of the size of the mold cavity after the tire is fitted therein, special measuring apparatus is dispensed with and it is unnecessary to have a chart for each make and size of tire.

I claim:

1. The method of fitting a pneumatic tire toi a retread vulcanizing mold which comprises diametrically measuring the tire periphery around the crown thereof and along parallel lines bridging its central space and tangent to the side walls, and placing it, with a raw tread thereon, in a fullcircle vulcanizing mold having a tire-receiving space with a xed transverse peripheral dimensio-n which is Within predetermined limits of variation of the measured tire periphery.

2. A method according to claim 1 in which the tire is measured with the raw tread thereon.

3. A method according to claim 1 in which the tire is measured when inilated on a rim and having a raw tread thereon.

4. The method of retreading a pneumatic tire which comprises rim-mounting and inflating the tire bearing the raw tread, diametrically measuring its included periphery around the tread and along side lines tangent to the side Walls of the tire, placing it in a full-circle vulcanizing mold having a cavity With an included diametric periphery of a i'lxed dimension which is within predetermined limits of variation or the measured tire periphery, the Walls of said cavity peripherally embracing the tire tread and tangently embracing its side Walls, leaving the base portions of the side Walls free to bulge, inlating the tire to a curing pressure Vin the mold, and vulcanizing the tread While the mold-embraced portions of the tire are held to the fixed dimensions of the mold cavity. Y

5. The method of tting a pneumatic tire casing to a retread vulcanizing mold which comprises providing tire-confining and tread-molding sections adapted collectively to form a series of fullcircle molding cavities of diierent capacities and xed dimensions and each of a predetermined diametric peripheral dimension including tangent inner marginal side portions of fixed spacing adjacent to a central open space, fixing the crosssectional dimension of the tire casing including its bead spacing and, While so fixed and by a single measurement, diametrically measuring the casing periphery around the crown thereof and along parallel lines bridging the central space and tangent to the side Walls, selecting and combining appropriate mold sections to form a tireccnning and tread-molding cavity of Xed capacity Whose corresponding measurement includes that of the tire casing Within predetermined limits of variation of the latter, and placing said casing, With a raw tread thereon, in the molding cavity for vulcanizing said tread.

JAMES C. HEINTZ. 

